当前位置：首页 > news >正文

Linux驱动学习-spi接口

news 2025/8/30 8:03:50

SPI驱动

SPI全称更是serial Peripheral interface的缩写，由美国摩托罗拉公司推出的一种同步串行传输规范。

1、特点

（1）SPI是一种高速，全双工，同步串行总线。

（2）SPI由主从两种模式，通常由一个主设备或者多个从设备组从。SPI不支持多主控i，

（3）SPI通信至少需要四根线，分别是MISO(主设备数据输入，从设备输出)，MOSI（主设备数据输出从设备输入），SCLK(时钟信号)，CS/SS（片选信号)

2、硬件连接

3、SPI通信原理

SPI主设备和从设备都有一个串行移位寄存器，主设备通过向SPI串行寄存器写入一个字节来发起一次数据传输。

举例：（可设置，默认先传输高位）

4、通信过程

5、SPI极性和相位

6、SPI子系统框架

绝大多数情况下，你只需要使用SPI核心层提供的API函数来编写你的具体外设驱动，而SPI控制器设备驱动层（你所说的“芯片原厂实现的部分”）通常已经由芯片厂商或主线Linux内核提供了。

当然，设备驱动层也可以学习一下怎么写的

6.1 spi外设代码框架编写：device部分

在没有设备树之前，是要用c代码的方式实现device部分的，非常麻烦，有设备树之后直接写就行：

6.2 spi外设代码框架编写：driver部分

#include <linux/init.h>
#include <linux/module.h>
#include <linux/spi/spi.h>

int mcp2515_probe(struct spi_device *spi)
{printk("This is mcp2515_probe\n");return 0;

}

int mcp2515_remove(struct spi_device *spi)
{printk("This is mcp2515_remove\n");return 0;

}

const struct of_device_id mcp2515_of_match_table[] = {{.compatible = "my-mcp2515"),{}
};

const struct spi_device_id mcp2515_id_table[] = {{"mcp2515"),{}
};

struct spi_driver spi_mcp2515 = {.probe = mcp2515_probe,.remove = mcp2515_remove,.driver = {.name = "mcp2515",.owner = THIS_MODULE,.of_match_table = mcp2515_of_match_table,},.id_table = mcp2515_id_table
};

static int __init mcp2515_init(void)
{int ret;ret = spi_register_driver(&spi_mcp2515);if (ret < 0) {printk("spi_register_driver error\n");return ret;}return ret;
}

static int __exit mcp2515_exit(void)
{int ret;ret = spi_unregister_driver(&spi_mcp2515);if (ret < 0) {printk("spi_unregister_driver error\n");return ret;}return ret;
}

module_init(mcp2515_init);
module_exit(mcp2515_exit);
MODULE_LICENSE("GPL");

下面我们通过追踪一下代码来看一下为什么没有进probe函数：

1、当spi的设备和驱动匹配成功会执行下面这个prboe函数

2、在这个prboe函数中，这段会注册一个spi控制器。

3、在spi_register_controller函数中调用了下面这个，会对设备树的属性进行提取

4、在of_register_spi_device函数中，看到下面函数：

5、在of_spi_parse_dt函数中，可以看到如果子节点一些属性没写，就会报错返回，所以就进不了probe函数了：

6、总结

编译后没有进probe函数，是因为dts没有添加相应属性，return掉了

所以dts应该配置如下：

7、实验硬件：mcp2515介绍

先了解一下mcp2515。

8、mcp2515驱动编写：注册字符设备

前面已经可以匹配进probe函数了，接下面就是完善驱动程序，可以在驱动程序注册一个字符设备，创建相应的设备节点

#include <linux/init.h>
#include <linux/module.h>
#include <linux/spi/spi.h>
#include <linux/cdev.h>
#include <linux/fs.h>
#include <linux/kdev_t.h>

dev_t dev_num;
struct cdev mcp2515_cdev;
struct class *mcp2515_class;
struct device *mcp2515_device;

int mcp2515_open(strct inode, struct file *file)
{return 0;
}

ssize_t mcp2515_read(struct file *file, const char __user *buf, size_t size, loff_t *offset)
{return 0;
}

ssize_t mcp2515_write(struct file *file, const char __user *buf, size_t size, loff_t *offset)
{return 0;
}

ssize_t mcp2515_relese(struct file *file, const char __user *buf, size_t size, loff_t *offset)
{return 0;
}

struct file_operations mcp2515_fops = {.open = mcp2515_open,.read = mcp2515_read,.write = mcp2515_write,.relese = mcp2515_relese,
};

int mcp2515_probe(struct spi_device *spi)
{int ret;printk("This is mcp2515_probe\n");ret = alloc_chrdev_region(&dev_num, 0, 1, "mcp2515");if (ret < 0) {printk("alloc_chrdev_region\n");return -1;}cdev_init(&mcp2515_cdev, &mcp2515_fops);mcp2515_cdev.owner = THIS_MODULE;ret = cdev_add(&mcp2515_cdev, dev_num, 1);if (ret < 0) {printk("cdev_add error\n");return -1;}mcp2515_class = class_create(THIS_MODULE, "spi_to_can");if (IS_ERR(mcp2515_class)) {printk("class_create error\n");return PTR_ERR(mcp2515_class);}mcp2515_device = device_create(mcp2515_class, NULL, dev_num, NULL, "mcp2515");if (IS_ERR(mcp2515_device)) {printk("device_create error\n");return PTR_ERR(mcp2515_device);}return 0;
}

int mcp2515_remove(struct spi_device *spi)
{printk("This is mcp2515_remove\n");return 0;
}

const struct of_device_id mcp2515_of_match_table[] = {{.compatible = "my-mcp2515"),{}
};

const struct spi_device_id mcp2515_id_table[] = {{"mcp2515"),{}
};

struct spi_driver spi_mcp2515 = {.probe = mcp2515_probe,.remove = mcp2515_remove,.driver = {.name = "mcp2515",.owner = THIS_MODULE,.of_match_table = mcp2515_of_match_table,},.id_table = mcp2515_id_table
};

static int __init mcp2515_init(void)
{int ret;ret = spi_register_driver(&spi_mcp2515);if (ret < 0) {printk("spi_register_driver error\n");return ret;}return ret;
}

static void __exit mcp2515_exit(void)
{device_destory(mcp2515_class, dev_num);class_destory(mcp2515_class);cdev_del(&mcp2515_dev);unregister_chrdev_region(dev_num, 1);spi_unregister_driver(&spi_mcp2515);

}

module_init(mcp2515_init);
module_exit(mcp2515_exit);
MODULE_LICENSE("GPL");

9、mcp2515驱动编写：复位函数

下面继续对上面的驱动进行完善：

9.1 配置dts:

上图红线内就是配置spi的模式，如果两个都没有注释，就是1 1，否则注释了就是0 0

上图红框内如果没有注释则代表spi从低位开始传输，注释了则代表从高位开始传输。

上图红框内如果没有注释则代表spi的cs片选脚是高电平选中，注释了则代表spi的cs片选脚是低电平选中。

最终配置：

2、添加复位函数

10、探究：SPI的通信流程

11、mcp2515驱动编写：读寄存器函数

#include <linux/init.h>
#include <linux/module.h>
#include <linux/spi/spi.h>
#include <linux/cdev.h>
#include <linux/fs.h>
#include <linux/kdev_t.h>

dev_t dev_num;
struct cdev mcp2515_cdev;
struct class *mcp2515_class;
struct device *mcp2515_device;

struct spi_device *spi_dev;

int mcp2515_open(strct inode, struct file *file)
{return 0;
}

ssize_t mcp2515_read(struct file *file, const char __user *buf, size_t size, loff_t *offset)
{return 0;
}

ssize_t mcp2515_write(struct file *file, const char __user *buf, size_t size, loff_t *offset)
{return 0;
}

ssize_t mcp2515_relese(struct file *file, const char __user *buf, size_t size, loff_t *offset)
{return 0;
}

struct file_operations mcp2515_fops = {.open = mcp2515_open,.read = mcp2515_read,.write = mcp2515_write,.relese = mcp2515_relese,
};

void mcp2515_reset(void)
{int ret;char write_buf[] = {0xc0};ret = spi_write(spi_dev, write_buf, sizeof(write_buf));if (ret < 0) {printk("spi_write is error\n");}
}

void mcp2515_read_reg(char reg) {char write_buf[] = {0x03, reg};char read_buf;int ret;ret = spi_write_then_read(spi_dev, write_buf, sizeof(write_buf), &read_buf, sizeof(read_buf));if (ret < 0) {printk("spi_write_then_read error\n");return ret;}return read_buf;
}

int mcp2515_probe(struct spi_device *spi)
{int ret;char value;printk("This is mcp2515_probe\n");spi_dev = spi;ret = alloc_chrdev_region(&dev_num, 0, 1, "mcp2515");if (ret < 0) {printk("alloc_chrdev_region\n");return -1;}cdev_init(&mcp2515_cdev, &mcp2515_fops);mcp2515_cdev.owner = THIS_MODULE;ret = cdev_add(&mcp2515_cdev, dev_num, 1);if (ret < 0) {printk("cdev_add error\n");return -1;}mcp2515_class = class_create(THIS_MODULE, "spi_to_can");if (IS_ERR(mcp2515_class)) {printk("class_create error\n");return PTR_ERR(mcp2515_class);}mcp2515_device = device_create(mcp2515_class, NULL, dev_num, NULL, "mcp2515");if (IS_ERR(mcp2515_device)) {printk("device_create error\n");return PTR_ERR(mcp2515_device);}mcp2515_reset();value = mcp2515_read_reg(0x0e);printk("value is %x\n", vlaue);return 0;
}

int mcp2515_remove(struct spi_device *spi)
{printk("This is mcp2515_remove\n");return 0;
}

const struct of_device_id mcp2515_of_match_table[] = {{.compatible = "my-mcp2515"),{}
};

const struct spi_device_id mcp2515_id_table[] = {{"mcp2515"),{}
};

struct spi_driver spi_mcp2515 = {.probe = mcp2515_probe,.remove = mcp2515_remove,.driver = {.name = "mcp2515",.owner = THIS_MODULE,.of_match_table = mcp2515_of_match_table,},.id_table = mcp2515_id_table
};

static int __init mcp2515_init(void)
{int ret;ret = spi_register_driver(&spi_mcp2515);if (ret < 0) {printk("spi_register_driver error\n");return ret;}return ret;
}

static void __exit mcp2515_exit(void)
{device_destory(mcp2515_class, dev_num);class_destory(mcp2515_class);cdev_del(&mcp2515_dev);unregister_chrdev_region(dev_num, 1);spi_unregister_driver(&spi_mcp2515);

}

module_init(mcp2515_init);
module_exit(mcp2515_exit);
MODULE_LICENSE("GPL");